Method of making preliminary shaping dies



Aug. 28, 1945. L. E. BURGER ETAL 2,383,706

METHOD OF MAKING PRELIMINARY SHAPING DIES Filed Febyzs, 1944 2Sheets-Sheet 1 INVENTOR. Aswxa E. BURGER JEN/wuss .B. d'k/NNERn-rronlvav 1945- L. E. BURGER ETAL I 2,383,706

METHOD OF MAKING PRELIMINARY SHAPING DIES I Filed Feb. 23, 1944 2Sheets-Sheet 2 Arron/45v Patented Aug. 2a, 1945 Mn'rnon or MAKINGrimmmuaar snarnvo pms Lewis E. Burger, La Mesa, and Jennings B. Skinner,San Diego, Calif asslgnors to Solar Aircraft Company, San Diego,Calli'., a corporation of California 1 Application February 23, 1944,Serial No. 523,516

oi-the art in 6 Claims. (Ci. 76-107) -This invention relates to the diestamping art in which metal sheetsare stretched and bent .into desiredshapesby pressing or striking them between dies,: and more particularlyto that phase which a plurality of sets of dies of successively greaterdepth are required to produce the desired shape. n

An object of the invention is to simplify the construction of dies foruse in the preliminary In the drawings:

Fig. l is a perspective view of a pattern for a finish die; A Fig. 2 isa cross section of the pattern of Fig. 1 taken in the plane IT-II andshowing a wax pattem sheet formed therein;

Fig. 3 is a perspective view of a pattern for a preliminary stage diemade in' accordance with the. present invention from the finish patternof stages of a multi-stage drawing or stamping oper- '10 Fig. 1; ation.v Fig. 4 is a cross section of the wax pattern Another object is toreduce the amount of skill sheet as it appea wh n r v r h P required toproduce effective preliminary dies. m f 181 2;

Another object is to provide preliminary dies Fls. 51s a cross sectionof the pattern sheet "or superior shape. in that they so prepare theafter it has been part lly flattened out. the sec-- sheet metal for thefinal dies that the latter can i n being taken in t e osi io c rr sponin produce deep and abrupt slopes without breaking t0 the line V-V ofFig. 3; or excessively thinning or wrinkling the metal. Fig. 6 is across section showing the p n -Heretofore, wheria stamping or drawingoper- Sheet 0! 8- Supported n r inf rced with ation of more than onestage was necessary in p order to produce. a satisfactory deep or abruptFig. 7 is a cross section showing the reinforced slope in a work sheet,it was the practice to have Pattern Sheet of a 6 n te ndmounted in thedies used in the prellminarystages made a D ready casting the pl r pa rn01 manually by highly skilled pattern makers who n produced them largelyby the process of trial and -r j' oil ign fieg ga sridsgggflross sectionof a a 3 32 w expenditure of a eIna-m; de 1 Referringfirst to Figs. 1and 2, there is shown In accordance with-the present invention, we aPlaster p n for m kin a female finish provide a routine procedure forpreparing predie for use ina drop hammer or the like for liminai-y diesfrom finish dies, greatly reducing Shaping Sheet m l- In accordance withwell the amount of time and skill required and yieldknown procedure. t edi may be cast in a sand ing dies more uniformly satisfactory than those-m01d. which mold was firs f m f m the p i'ormerly made by highlyskilled pattern makers. tern l0. insofar as the present invention iscon- I The present invention is based on the prin- 35 rn d, either thepattern ll or the finish die ciple that the preliminary drawing orstamping formed therefrom can be employed since both are operations..should soshape the sheet that the of identical shape. It is usuallymost convenfinal operation is largely .a bending operation, ient toemploy the plaster pattern It. involving. relatively little stretchingor compres- It is to be understood that in the stamping press '-sion of.the sheet. Hence, we make the prelim- 40 or drop hammer, amale die orpunch isemployed inary ,dies with substantially the same absoluteand'that the sheet metal to be shaped is pressed areae-as-the ilnal diebut having less depth so or struck between the male and female dies.that the projected area is greater. This result However, it is customaryto make the male die is obtainedeby-using as a pattern i'ormaking the orpunch from the female die, and hence, it is preliminary die asubstantially non-stretchable, sufli'cient in connection with thepresent invenfiextble. sheet that has been-first shaped in the tion todisclose the method. or preparing the patflllishidie and then flattenedou y i g tern for only the femaledie, the. latter being reduce itsdepth. A suitable material for such hereinafter referred to as the.die."asheet is waxreinforced by fabric in such a Ther is shown in Fig. 3 a,plaster pattern ll way as to prevent it from stretching or shrinki 5 forforming the preliminary die which is used to while permitting it tobend. shape the sheet metal before it is placed in the "A fullunderstanding of the inven i n m y be finish ,die corresponding to thepattern ill of had from the following detailed description wit .Fig. 1.It will be observed that the pattern ll of reference to the-drawings ofa specific procedure Fig. 3 beats little resemblance to-the pattern illin accordance with the invention.

of Fig. 1, yet the shape of pattern II is inherently such as to preparethe sheet metal (or stamping in the finish die so that it can take theform of the finish die without breamng and without thinning or wrinklingexcessively. The reason for this is that the total surface of thepattern H is substantially the same as that of Fig. 1, the depth ofpattern H being substantially less and the projected areacorrespondinglyv greater. Pattern ii is obtained in accordance with thepresent invention by the following procedure:

First there is formed in the finish pattern id a thin pattern sheet I:of wax reinforced with cheesecloth. This is done by first painting thesurface of the plaster pattern I! witha thin paint of modeling clay,liquid soap and water to prevent the pattern sheet I! from sticking tothe plaster. Before this paint has dried, a first sheet 13 (Fig. 8) ofcheesecloth is placed on the pattern IB and pressed into intimatecontact with the surface thereof, the cheesecloth being sumcientlyyielda-ble to permit such shaping.

Next, the cheesecloth It is coated with a suit able wax It by applyingit on top of the cheesecloth 13 in melted condition with a brush. At thesame time the cheesecloth is again forced into all the corners of thepattern with the brush. This wax congeals as soon as it is applied tothe cheesecloth by virtue of conduction of heat therefrom into theplaster pattern, and by repeated applications of the molten wax with thebrush, the layer it oi wax is built up to a depth of approximately a; ofan inch.

Next, a second sheet of cheesecloth i is pressed into the wax Id whilethe latter is relatively soft, this second sheet id being laid on thebias with respect to sheet 53; that is, with its threads running atapproximately 45 with respect to the threads of cloth i3. Thereafter, afinal thin coat it of wax is brushed on 'to the cloth 16, therebycompleting the pattern sheet i2 as shown in Fig. 2.

After it has cooled a little more and becomes fairly stiff, the patternsheet i2 is removed from the pattern l9 by gradually pulling it awaytherefrom with the hands. It comes away quite readily because of thethin coat of modelin clay, liquid soap and water that was placed on theplaster pattern before the pattern sheet was formed. As removed from thepattern id, the pattern sheet I2 appears as shown in Fig. 4, having theshape of the finish pattern lb. It is then flattened out into the shapeshown in Fig. 5. this flattening operation being performed by pullingthe pattern sheet apart with force appliedat juxtaposed points on theedge thereof accompanied by slight force applied to the under side oithe intermediate portion with the hands. This operation changes theshape of the pattern sheet without appreciably changing its area becausethe two sheets of cheesecloth laid on the bias with respect to eachother largely prevent stretching of the pattern. Such stretching couldnot be avoided if the pattern sheet were made of wax alone without anyfabric reinforcement.

After the pattern sheet has been flattened as shown in Fig. 5, it isused to cast the preliminary stage plaster pattern shown in Fig. 3 bythe procedures illustrated in Figs. 6 and 7.

Referring to Fig. 6, the pattern I: is first supported at. relativelyclosely spaced points on its under surface by means of clay bolsters i1ex tending upwardly from a supporting table or base l8, after which athick layer IQ of plaster of Paris is appliedto the upper surface of thepattern sheet, this layer I9 being formed by applying plaster inrelatively still condition with a trowel, or with the hands. 7

After the plaster backing 19 has set, the assembly of the pattern sheet12 and the backing i9 is removed from the clay bolsters i'I, invertedand supported on clay bolsters 28 extending upwardly from a base 2| asshown in Fig. 7. Thereafter, side walls 22 of wood or other suitablematerial are constructed around the plaster backed pattern sheet to formtherewith a mold into which liquid plaster of Paris can be poured. Whenthis plaster of Paris has solidified and has been removed from the mold,it constitutes the preliminary pattern of Fig. 3.

It will be observed from the procedure described that the inventionprovides a routine process for developing patterns for preliminary diesfrom patterns of finish dies, requiring very little special skill.Furthermore, the procedure is relatively simple and does not requiremuch time,

In some cases, it is necessary to employ more than one preliminary dieto bring the sheet metal into the final desired form by successivestages.

each involving a relatively small change in shape from the nextpreceding stage. Hence, in some instances, it may be desirable to forman intermediate stage pattern from the final pattern and then form afirst stage pattern from the intermte stage pattern. Under suchconditions, the intermediate stage pattern can be prepared as described,after which a first stage pattern can be prepared from the same waxpattern by further flattening it and increasing its projected area andthen using it to make the mold for easting the first stage pattern.

Although various waxes may be employed in forming the pattern sheet i2,a composition that has been found suitable in practice consists of amixture of from one-half to two-thirds beeswax with the balance apattern. maker's wax such as "Master sheet wax made by Kindt-Collins Co.

of Cleveland, Ohio. If overheated, the wax may become too hard, underwhich condition it may be softened with the addition of a small amountof turpentine.

Various departures from the exact procedure described may be made, whilestill obtaining the advantages of the invention, and the latter istherefore limited only to the extent set forth in the appended claims.

We claim:

1. In the art of sheet stamping and drawing, the method of preparing apreliminary shaping die from a later stage die, said method comprisingthe steps of: first, forming in said later stage die a flexible,substantially non-stretchable and non-compressible sheet pattern;second, removing said sheet pattern from said later stage die andpartially flattening it to reduce its depth and increase its projectedarea withoutmaterially changing its absolute area; and third, using saidflattened sheet pattern as a mold to reproduce its shape in thepreliminary shaping die to be prepared.

2. In the art of sheet stamping and drawing, the method of prepar g aina y s pin die from a later stage die, said method comprising the stepsof: pressing against said later stage die a sheet of readily deformablefibrous material and coating it with plastic wax and permitting the waxto congeal; second, removing said sheet of deformable material coatedwith wax from said later stage die and partially flattening it to reduceits depth and increase its projected area without materially changingits absolute area; and third, using said partially flattened sheet as amold to reproduce its shape in the preliminary shaping die to beprepared.

3. In the art of sheet stamping and drawing, the method of preparing apreliminary shaping die from a later stage die, said method comprisingthe steps of: first, placing against said later stage die a first sheetof textile material; second, coating said sheet with heated plastic wax;three, pressing a second sheet of textile material on to said wax whilethe latter is still soft with the threads of said second sheet oftextile material extending diagonally with respect to the threadsflexible, plastic material reinforced with sheet textile material,

5. Th method described in claim 1 in which said sheet pattern consistsof a layer of wax reinforced with a plurality of sheets of textilematerial laid on the bias with respect to each other.

6. In the art of sheet stamping and drawing the method of preparing aplurality of preliminary shaping dies of successively greater depth froma later stage die, said method comprising the steps of: first, formingin said later stage die a flexible substantially non-stretchable andnoncompressible sheet pattern; said sheet pattern from said later stagedie and partially flattening it to reduce its depth and increase itsprojected area without'materially changing its absolute area; third,using said partially flattened sheet pattern as a mold to reproduce itsshape in an intermediate stage shaping die to be prepared; fourth,further flattening said sheet pattern to further reduce its depth andincrease its projected area withoutv materially changing its absolutearea; and fifth, using said further flattened sheet pattern as a mold toreproduce its shape in the first stage die to be prepared.

LEWIS E.- BURGER. JENNINGS B. SKINNER.

second, removing

